F. Lange, P. Judeinstein, C. Franz, B. Hartmann-Azanza, S. Ok, M. Steinhart, K. Saalwächter.
Diffusion of Entangled Polymers along Nanochannels
ACS Macro Lett. 4, 561-565 (2015).
Changes in large-scale polymer diffusivity along interfaces,
arising from transient surface contacts at the nanometer scale, are not
well understood. Using proton pulsed-gradient NMR, we here study the
equilibrium micrometer-scale self-diffusion of poly(butadiene) chains
along ~100 Ám long, 20 and 60 nm wide channels in alumina, which is a
system without confinement-related changes in segmental relaxation
time. Unlike previous reports on nonequilibrium start-up diffusion
normal to an interface or into particulate nanocomposites, we find a
reduction of the diffusivity that appears to depend only upon the pore
diameter but not on the molecular weight in a range between 2 and 24
kg/mol. We rationalize this by a simple volume-average model for the
monomeric friction coefficient, which suggests a 10-fold surfaceenhanced
friction on the scale of a single molecular layer. Further
support is provided by applying our model to the analysis of published data on large-scale diffusion in thin films.